Q&A for How to Texture Paint

You can. However, it likely won't look too good, and you run the risk of oversaturating the wallpaper and the glue could give way. Normally wallpaper is removed before painting.

It depends on the thickness of the wallpaper itself and what kind of texture you are going to use on your surface.

Silica sand is quartz, technically. You can get it at the hardware store or Amazon, or perhaps the craft store. I've used real sand in paint projects when I was a kid and it worked well to create a sandy, textured surface, so if you have a beach nearby, just go grab a tub of sand from there and experiment with one of those little $2 tester paints from the hardware store. You can even have them colored.

If you do, you're going to need to create a solid base with a primer, first. Otherwise, you'll end up with a texture you probably don't want, as the paint separates and sticks to itself instead of the aluminum.